538 now reporting that GOP control of the Senate is becoming increasingly improbable.

"Democrats are now favored to retain control of the Senate when the new Congress convenes in January, according to the FiveThirtyEight forecast, breaking a summer stalemate during which control of the chamber appeared about equally likely to go either way.

An unusually large number of Senate races remain competitive, meaning that a wide range of outcomes are still possible. Republicans have about a 10 percent chance of winning a net of at least six seats from Democrats, according to the forecast, which would give them control of at least 53 seats next year. However, there is also about a 20 percent chance that Democrats could actually gain Senate seats on balance, giving them at least 54. The only thing that seems completely assured is that neither party will control enough seats next year to hold a filibuster-proof majority."